Add configure option --disable-some-floating-point

See discussion here: http://lists.freedesktop.org/archives/cairo/2006-November/008602.html

configure.in

@@ -773,6 +773,29 @@ fi
 
 dnl ===========================================================================
 
+AC_ARG_ENABLE(some-floating-point,
+  AS_HELP_STRING([--disable-some-floating-point],
+                 [Disable certain code paths that rely heavily on double precision
+                  floating-point calculation. This option can improve
+                  performance on systems without a double precision floating-point
+                  unit, but might degrade performance on those that do.]), [
+if test "x$enableval" = "xno"; then
+  # A value of 'no' for $enableval means that they want to disable, which
+  # means 'yes' for $disable_some_floating_point.
+  disable_some_floating_point=yes
+fi
+])
+
+AM_CONDITIONAL(DISABLE_SOME_FLOATING_POINT,
+               test "x$disable_some_floating_point" = "xyes")
+if test "x$disable_some_floating_point" = "xyes"; then
+  AC_DEFINE(DISABLE_SOME_FLOATING_POINT, 1,
+            [Define to 1 to disable certain code paths that rely heavily on
+             double precision floating-point calculation])
+fi
+
+dnl ===========================================================================
+
 AC_CONFIG_COMMANDS([src/cairo-features.h],
 [
 	featuresfile=src/cairo-features.h